[Openstack] How does VMs connect to cinder created Volumes ?

Marco CONSONNI mcocmo62 at gmail.com
Wed Dec 5 10:34:43 UTC 2012


As far as I understand, the communication between a VM, running on a node,
and a volume, 'running' on another node, is carried out bu open-iscsi
(ISCSI client running on the node where you run the VM) and tgt (iSCSI
server running on the node where you host the volumes).

Cinder's daemons, in particular cinder-volume, just issue commands for tgt
to create volumes and making them available on the network.
After that, when you connect  a volume to a VM, very likely the Hypervisor
is instructed to retrieve the volume through the iSCSI client.

Anyway, I found out that:

-- the node that host the storage MUST run both tgt and cinder-volume
-- cinder-scheduler and cinder-api can be deployed on any other node
-- any compute node MUST run open-iscsi (iSCSI, client) in order to access

Hope it helps,

On Wed, Dec 5, 2012 at 10:53 AM, Skible OpenStack <
skible.openstack at gmail.com> wrote:

> Hello everyone,
> I have cinder installed on my controller node, can anyone explain to me
> how a VM becomes aware of the volume ?
> After all a VM is launched on a node different than the controller one so
> if the VM wants to store something on the Volume, does it have to send the
> data to the controller node which in his turn will save the data on the
> volume using cinder or is there a direct connection between the VM and the
> volume after allocation, if yes, is this connection on the hypervisor level
> or what level exaclty?
> Thanks, really appreciate it if you can help me out there !
> Best regards
> Fellow Stacker
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